Filter headers are used in electronic module applications as a means for controlling electromagnetic interference (EMI). Many of these filter headers include a ferrite block for electrically filtering of high frequency signals and surface-mounted chip capacitors to provide a low impedance path-to-ground for high frequency signals. Some designs use spring contact members to interconnect the capacitor from the electrical terminals to ground. Other designs use an additional substrate layer which adds complexity to the manufacturing process. The present invention is based upon capacitors mounted directly on the plated surface of a connector body thus forming a three-dimensional printed circuit which greatly reduces the number of components of the assembly resulting in less cost and less manufacturing complexity.
However, the placement of chip capacitors on connector bodies poses unique problems when compared to similar designs on a flat printed circuit board. A primary failure mode for chip capacitors soldered to a substrate occurs during thermal cycling. The difference in the coefficient of thermal expansion between the substrate material and the ceramic chip capacitor creates stress in the solder fillet connecting the capacitor to the substrate. This problem is amplified when the substrate is a plated plastic connector body. The plastic connector body produces transient thermal gradients which result in localized failures of the solder fillets. The plastic materials typically have a greater coefficient of thermal expansion than that of typical printed circuit board materials. Furthermore, the basic connector body results in nonuniform thickness of the substrate area beneath the chip capacitor. Solutions to this problem would preferably have the ability to be incorporated into an existing package size, which in turn would allow the utilization of existing automated assembly equipment and also allow the filtered headers to be used interchangeably with existing non-filtered header connectors.
The present invention provides advantages over the prior art.